The four ventricles of the human brain are interconnected cavities that produce and circulate cerebral spinal fluid (CSF). Procedures involving ventriculostomy, i.e., placement of a catheter into the ventricular system of the brain, form a major part of a neurosurgeon's clinical practice. General areas of application of ventricular catheter placement include intracranial pressure monitoring (ICP), draining or shunting of CSF and the instillation of pharmacological therapeutic agents.
CSF drainage is essential for patients with congenital or acquired hydrocephalus. CSF drainage, which can only be performed with an intraventricular catheter, is a life-preserving procedure, because it can immediately reduce intracranial pressure. The ventricular catheter, used to drain CSF, is connected to a peripheral subcutaneous drainage system, i.e., to the peritoneal cavity or systemic circulation via the heart or in the case of ICP to an external drainage collection system. Standard procedures for ventricular catherization are disclosed in the textbook literature. See, for example, Neurosurgery, edited by Robert H. Wilkins and Setti S. Rengachary, Section A, Chapter 13, Techniques of Ventricular Puncture (McGraw Hill 1984).
The most frequently chosen site for ventricular catheterization is coronal. In most cases, a catheter is inserted in the anterior horn of the lateral ventricle through an orifice or burr hole drilled just anterior to the coronal suture in the midpupillary line of the cranium, i.e., in the frontal bone over the ventricle. This is known in the field as Kocher's point. The burr hole, only slightly larger than the diameter of the selected catheter to insure a snug fit and provide a seal against CSF leakage, is placed approximately 1 cm anterior to the coronal suture, approximately 10 to 12 cm above the nasion, and approximately 2 to 3 cm from the midline over the nondominant hemisphere. After the burr hole is made, the dura and underlying pia-arachnoid are opened and coagulated, for example, with a fine-tipped blade after cauterizing the dural surface.
The lateral ventricles of the human brain form an arc parallel to the arc of the cranium, i.e., the contour of the lateral ventricles parallels the arc of the surface of the skull. Thus, a catheter guided perpendicular to the cranial surface at the point of entry into the cranium will enter the ventricular system. Specifically, any line penetrating a burr hole in the surface of the skull at a 90.degree. angle also bisects the lateral ventricle.
A more recently developed procedure to ensure correct catheter placement is disclosed in U.S. Pat. No. 4,613,324. The apparatus comprises a guide assembly which, when positioned over an orifice drilled in the cranium above the anterior horn of the lateral ventricle, guides a catheter and obturator through the orifice and into the lateral ventricle at an angle normal to an imaginary plane formed by a tangent to the cranium at the orifice, while the corresponding method comprises providing an orifice in the cranium just anterior to a coronal suture in a midpupillary line of the cranium and inserting a ventricular catheter containing an obturator through the orifice towards a lateral ventricle, wherein the catheter containing the obturator is guided through the orifice, by means of a novel guide assembly, at an angle normal to an imaginary plane formed by a tangent to the cranium at the orifice.
A wide variety of catheters are known in the prior art for the purpose of penetrating the ventricular cavity. Such catheters are typically in the form of a hollow tube with a circular bore which is provided with a plurality of apertures at the ventricular or inflow end to permit the passage of CSF from the brain into the catheter and thence to the bloodstream or peritoneal cavity of the patient or to an external drainage system. However, malfunctions frequently occur with such a catheter due to the blockage of the apertures in the inflow end of the catheter. Such blockage is usually caused by the growth of choroid plexus or ependymal tissue within the ventricle into the apertures in the inflow end of the catheter. This tissue may block the apertures in the inflow end of the catheter in a relatively short period of time after the catheter has been inserted into the ventricle thereby rendering the cathether inoperative in relieving excess pressure due to the build-up of CSF within the ventricle. Furthermore, prior art catheter apertures are cut perpendicular to the length of the catheter, thus causing abrasion of brain tissue when the catheter is inserted.
The likelihood of ventricular catheter malfunction by aperture plugging with brain tissue can be lessened by angling the aperture holes in the wall of the catheter such that there is "no see through" flow from the outside to the inside of the lumen. Also, by positioning the rows of apertures 120.degree. apart there is essentially no chance for direct ingrowth of ventricular tissue therethrough. In addition, the apertures are angled away from the direction of the insertion of the catheter into the brain thus lessening the chance of brain abrasion. Further, by slightly stretching the catheter by means of the stylet (which is integral to the catheter and used for placement of it into the brain) the holes will close so that no opening will be visible during the placement thereof, with the holes re-opening after the tension on the catheter is relieved by removal of the stylet.
A catheter may also malfunction by kinking due to insufficient structural rigidity. Kinking may cause blockages or ineffective flow paths within the catheter, thereby rendering it inoperative in relieving excess pressure due to the build-up of CSF within the ventricle. In addition, kinking may cause the catheter to wander off course and make the insertion more difficult for the neurosurgeon and more harmful to the patient. The likelihood of the catheter kinking can be lessened by using a non-circular bore which will increase structural rigidity and strength.
As such, it would be desirable to provide a catheter which overcomes the problems of previously devised ventricular catheters which are emplaceable within a ventricle of a human brain to control the flow of excess fluids to or from the brain. The present invention provides a simple solution which resolves the problems of prior art catheters in a novel and unexpected manner.